Play multiple .mcap files locally in Foxglove as if they were a single file.
Every experiment, test run, or deployment in robotics development generates massive amounts of data that you must analyze to debug issues, refine algorithms, and validate performance. However, when these logs are spread across multiple files—a common occurrence due to rolling recording systems or topic-specific logging—working with them can become an unnecessary headache. Traditionally, viewing these files as a single dataset meant manually merging them into a unified .mcap file before playback. This extra step added friction, consuming time and resources that could be better spent improving your robots reliability.
Instead of manually merging files, you can now open multiple .mcap files locally in Foxglove–a feature that has long existed within Foxglove’s data management capabilities–and it will seamlessly handle synchronization and playback, presenting the data as if it were loaded from a single, unified file. This means that whether your files were split due to rolling recording or topic-based logging, they can be played back together instantly, without any manual pre-processing.
There’s no need to waste time writing merging scripts, or managing duplicate files just to get a unified view of your data. Foxglove enables you to focus on debugging, analysis, and iteration rather than local file management. When you’re working with large datasets, this simple yet powerful improvement makes a tangible difference in your daily workflows.
Before local multi-file playback, manually merging .mcap files was necessary to ensure that different data streams—such as lidar scans, camera images, IMU readings, and actuator states—were correctly synchronized. The standard way to merge .mcap files involves using the MCAP CLI and running:
mcap merge --output merged.mcap file1.mcap file2.mcap file3.mcap
This workflow, while effective, is somewhat of an inconvenience. Manually merging large .mcap files takes time, often delaying your debugging process. Any mistake—such as omitting a file—could lead to incorrect analysis, forcing you to start over. The storage impact can also be significant. Since merging effectively duplicated data, disk space could quickly become a problem.
Consider a scenario where you’re testing an autonomous vehicle in an urban environment. Your logging records lidar point clouds, stereo camera images, and GNSS localization data, each saved as separate .mcap files. Partway through the test, the vehicle unexpectedly swerves at an intersection, and you need to diagnose why.
In the past, analyzing this event would require merging all relevant log files before you could even begin playback. Now, that extra step is unnecessary. You simply open the lidar, camera, and GNSS logs in Foxglove, and multi-file playback ensures that all streams remain synchronized. This lets you immediately correlate sensor data with vehicle behavior, dramatically accelerating the debugging process.
Stop wasting time merging .mcap files—visualize multiple .mcap files with just a few clicks. Whether you’re debugging perception algorithms, tuning motion planning, or verifying sensor calibration, you can quickly transform raw data into meaningful insights, streamlining your workflow like never before.
Check out the changelog, Download Foxglove now to give it a try, and join the community to share your work or give us feedback.
